In today's highly regulated telecommunications environment, network usage billing is governed by a complex set of rules and local access and transport area (LATA) tariffs. In order to properly abide by these rules and tariffs, calls are normally routed over trunk groups that have been designated and configured to carry the particular call types. Examples of calls that have different tariffs include local calls, interLATA-interstate calls, interLATA-intrastate calls, intraLATA-interstate calls, intraLATA-intrastate calls, etc. In practice, this complex tariff structure coupled with a large number of service providers and an associated array of complex interconnection agreements provides ample opportunity and incentive for calls to be inappropriately routed to their destinations. While such inappropriately routed calls may be the result of unintentional, erroneous routing translations in the network, all too often, such call routing is the result of a service provider trying to take advantage of the complex tariff structure by exploiting the call routing limitations of current telecommunication networks.
For example, switches in the public switched telephone network (PSTN) route calls based solely on the called party number that is contained within the call setup messages exchanged between switches. In other words, network switching elements make no attempt at determining the call type (e.g., local, interLATA-interstate, etc.). Hence, it is entirely possible for a network operator, intentionally or otherwise, to route any call type over any inter-switch trunk group.
It is possible, for instance, that calls which are non-local in nature may be routed over local trunk groups, thereby avoiding LATA access charges. An example of such a call scenario is depicted in FIG. 1. In FIG. 1, an exemplary telecommunication network 100 includes a core PSTN network 102, a tandem switching office 104 owned by Service Provider B, an end office 106 owned by Service Provider A, and a tandem switching office 108 owned by Service Provider C. An access trunk group 110 connects tandem switching office 104 and end office 106, while a local trunk group 112 connects tandem offices 104 and 108, and a local trunk group 114 connects tandem office 108 and end office 106. Network 100 also includes a calling party 116, and a called party 118, where the called party 118 is served by end office 106.
For purposes of illustration, it is assumed that a call placed from calling party 116 to called party 118 is not a local call, and consequently should be subject to inter-LATA tariff charges. Accordingly, a call from calling party 116 to called party 118 should be routed from Service Provider B's tandem office 104 to the terminating end office 106 of Service Provider A via the access bearer trunk group 110 that has been designated to carry non-local call traffic. However, as indicated in FIG. 1, Service Provider B may intentionally or otherwise route the non-local call to called party 118 via tandem office 108 over local bearer trunk groups 112 and 114. As such, a non-local call may be completed between calling party 116 and called party 118 without using the access trunk(s) that have been designated to handle such non-local traffic by Service Provider A.
In cases where such misrouting is performed intentionally for financial gain, the service provider perpetrating the fraud may modify one or more fields in a call setup signaling message, such as a signaling system 7 (SS7) ISDN user part (ISUP) initial address message (IAM), so as to make the fraudulent routing difficult to detect. FIG. 2 illustrates an ISUP IAM message 130, which includes a calling party number (CgPN) parameter 132, a called party number (CdPN) parameter 134, and a jurisdiction information parameter (JIP) 136, and a carrier identification code (CIDC) parameter 138. One or more of these parameters may be modified in order to misroute a call and to hide the fact that fraudulent routing has occurred. For example, the JIP and/or calling party number parameters may be hidden or erased to prevent source identification for source-based billing.
FIG. 3 is another view of network 100 that includes both bearer and signaling trunks. More particularly, signaling trunk 120 connects switches 104 and 108, signaling trunk 122 connects switches 106 and 108, and signaling trunk 124 connects switches 104 and 106. In an SS7 network, IAM call setup messages are used by switches to select bearer trunks (e.g., bearer trunks 110, 112, 114) and determine how a call will be routed within the network. In the sample call scenario depicted in FIGS. 1 and 2, if Service Provider B intends to route a call via local trunks 112 and 114, IAM signaling messages are communicated from Service Provider B's tandem office 104 to Service Provider C's tandem office 108 via signaling trunk 120 and eventually to the terminating end office 106 via signaling trunk 122. As described above, inter-carrier billing is often based on call origination information (e.g., calling party number, JIP parameter, etc.) Consequently, before misdirecting a call setup IAM message (as shown in FIG. 2) and enabling the call to be completed without using the appropriate access trunk group 110, Service Provider B's tandem office 104 may erase or alter a JIP or calling party number parameter contained in the call setup message. These parameters may be modified by Service Provider B in such a manner that it is not possible to determine the origin of the call, and, consequently, it is not possible for Service Provider A to determine that misrouting has occurred and/or the type of tariff to apply to the call.
The financial implications of such fraudulent routing may be substantial to a network operator. A typical routing arrangement associated with the network environment illustrated in FIG. 1 might require Service Provider B to pay Service Provider A terminating access charges in the range of $0.01 to $0.03 per minute for the call from calling party 116 to called party 118. Whereas, in the case where an inter-LATA call is routed over local trunk groups, Service Provider B may only be required to pay a fraction of this per minute charge to Service Provider A, if anything at all. The case where a call is intentionally misrouted to avoid tariffs is referred to as “arbitrage.” However, the term “arbitrage,” as used herein, is intended to include both the intentional and non-intentional misrouting of calls.
Accordingly, there exists a long felt need for improved methods and systems for detecting, mitigating and preventing fraudulent or otherwise misrouted calls in a telecommunications network.